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The objectives of this study were to investigate the relationship between permeability of chipseals, waterfilm thickness, basecourse moisture sensitivity, heavy traffic volumes, and premature pavement failure following construction through the use of accelerated pavement testing at CAPTIF.

The research has produced some surprising results in that the traditional M/4 basecourse was the worst performer in all cases. However, it must be borne in mind that this research can only be considered applicable to first coat seals, with high water film thicknesses at very high traffic volume.

The recommendations resulting from the research are to:

• prime all new pavements before first-coat sealing to reduce the risk of early failure
• condition new seals before they are loaded in wet conditions, ie avoid the practice of sealing just before it rains as this is likely to increase the probability of failure
• avoid geometric designs that generate large water film thicknesses
• not delay in placing second-coat seals on high-volume roads
• use unsaturated hydraulic models for modelling moisture movement in pavements
• review first-coat seal failures for the factors observed in this report
• undertake field trials of lower permeability M/4 alternatives.

Keywords: accelerated pavement testing, CAPTIF, chipseal, unbound pavements, water